Articles constructed of plastics are sometimes used in situations wherein it is essential to confine a liquid to a certain portion of the article to regulate dispensing of the liquid, to accurately measure the volume of the liquid, or the like. An illustration of such needs is found in connection with the toilet tank additive dispenser shown in U.S. Pat. No. 4,208,747, which issued to Robert S. Dirksing on June 24, 1980, wherein a passageway providing a bubble lock is used to isolate the product solution from toilet tank water in a syphon tube during non-flush periods. The present invention involves the recognition that when such a dispenser is constructed in a preferred manner, wherein the same comprises heat sealable thermoplastic sheets one or more of which are formed sections defining the chambers and passageways therein and with fin-type heat seals bordering the bubble lock passageway, leakage of the product solution to the toilet tank water can occur. The present invention further involves the discovery that such leakage is due to capillary transport of the product solution alongside the fin-type heat seals and the development of a structure designed to eliminate the problem.
Similar problems are believed to be found in connection with fin-type heat seals bordering the passageway of disposable hospital type fluid measuring devices, e.g. urinalysis bags.
The discovered art does not disclose recognition of the problem or the concept of the present invention's solution. For example, the aforementioned Dirksing patent describes constructing the passive dosing dispenser from two sections of material, one or both of which can be thermoformed, and sealed to each other by heat sealing, adhesives, etc., but does not indicate the potential problem of capillary transport.
Some prior art patents are directed to heat sealing through intermediate layers of materials. Bellamy Jr., U.S. Pat. No. 3,403,064, issued Sept. 24, 1968, concerns a method of forming a composite plastic container with an inner and outer seal, thus forming a container within a container. The laminates of polyvinyl chloride and polyhalohydrocarbon are assembled with the polyhalohydrocarbon faces in contact and radio frequency energized sealing dies used to join them. The heat melts and softens the PVC and polyhalohydrocarbon and the pressure of the dies forces the PVC through the polyhalohydrocarbon, forcing it out of the area between the dies. The PVC layers become heat sealed between the dies and the polyhalohydrocarbon layers unite in an inner seal alongside the PVC heat seal. Mark et. al., U.S. Pat. No. 2,341,845, issued Feb. 15, 1944 relates to a carton in which the closure flaps have sealing surfaces which are provided with a layer of heat-activatable adhesive covered by a layer of a wax composition. When the carton is sealed the sealing surfaces are heated, melting the wax layer and making the adhesive tacky, and pressed together. The molten wax flows from between the flaps and collects at the sides of the flaps, forming additional seals.
Fielibert, U.S. Pat. No. 3,679,509, issued July 25, 1972, on the other hand, teaches a process for sealing laminated materials for food containers. The laminates sealed are each polypropylene coated aluminum foil and are arranged with the coatings in contact. One of the heat sealing jaws is crowned so as to exert the greatest pressure along the center line of the heat seal area. When applied, the polypropylene layers retract from the center zone and form integral seals on each side of the parting line. As mentioned above, however, none of these references teach the problem or solution of the present invention.
It is an object of the present invention to obviate the above described problem.
Another object of the present invention is to provide an effective, economical fin-type heat seal joint for use in assembling articles wherein liquids must be confined to certain locations.
It is a further object of the present invention to provide a device employing fin-type heat seals to define a passageway and wherein such passageways are resistant to capillary transport by liquids contacting an end of the same.